Update pipeline .NET versions

Author: Carl-Hugo

.github/workflows/master.yml

@@ -38,9 +38,8 @@ jobs:
         uses: actions/setup-dotnet@v4
         with:
           dotnet-version: |
-            6.x
-            7.x
             8.x
+            9.x
 
       - name: Build
         run: dotnet build -c ${{ env.BUILD_CONFIGURATION }}
@@ -60,9 +59,8 @@ jobs:
         uses: actions/setup-dotnet@v4
         with:
           dotnet-version: |
-            6.x
-            7.x
             8.x
+            9.x
 
       - uses: dotnet/nbgv@master
         with: